The Digital Video Broadcast (DVB) standards and the Digital Satellite System (DSS) standards are designed for the delivery of digital video and digital audio “programs” to in-home set-top box appliances. More recently, interest has arisen in using these standards for high bandwidth data delivery, for example, to personal computers for applications such as Internet access. The data broadcast may include, for example, internet protocol (IP) packets carrying electronic mail, world wide web content, and other data.
In data broadcast systems, various elementary streams of digital video, digital audio, and digital data typically are time-division multiplexed onto a single transport stream that is broadcast by way of a satellite transponder to multiple receivers. The elementary streams of information or data are generally packetized, as is the transport stream.
A receiver, for example, may be coupled to a personal computer. Such a receiver would receive the transport stream comprising the information, demultiplex elementary streams of digital video, digital audio, and/or data from the transport stream, and filter (select) those elementary streams destined for that receiver. The receiver further should be able to deliver the elementary streams to host memory of the personal computer for processing or display.
Packets containing the elementary stream data may be addressed either to a single receiver, referred to as pointcasting, or to a group of receivers, referred to as multicasting. The address information is generally contained in a field of the header of each packet. The field containing the address information may be referred to as a media access control (MAC) field. The MAC field allows a receiver to store or process only the packets destined for that receiver.
Designing a receiver capable of demultiplexing, filtering, and delivering the elementary streams of information poses difficult problems and challenges. For example, critical timing constraints govern the delivery of elementary streams containing digital video and digital audio programs. These critical timing constraints derive, for example, from the specific timing required for proper decoding and presentation of digital video frames on the host computer. Hence, the particular elementary streams must be demultiplexed, filtered, and delivered in real time in such a way that these critical timing constraints are met.